The programmed responses of cells to environmental cues ultimately must require the coupling of extracellular signals to intracellular effectors. While this coupling undoubtedly involves a cascade of molecular events, little is known about specific pathways by which environmental signals are transduced. The concerted actions of early intracellular signals represented by expression of early response genes may mediate the responses of cells to their environment. Depending on the suite of early response genes expressed, cells would become committed to particular short or long- term activities. In the sea star, Asterias vulgaris, the investigators know that the annual initiation of spermatogonial mitotic divisions is ultimately under the control of light and that expression of a c-myc gene with functional domains remarkable conserved in comparison to mammalian c- myc is correlated the S-phase of the spermatogonial cell cycle. The major objective of studies outlined in this proposal is to determine if the c- fos, ornithine decarboxylase (ODC) and c-myc genes constitute such a suite of early response genes expressed during light-induced spermatogonial G1/S- phase traverse. Whether expression of these genes is actually interrelated during spermatogenesis is currently unknown for any animal. However, in mammalian somatic cellular systems, these genes are often co-expressed early in the response to a variety of molecular stimuli and, regardless of the signal, their expression is correlated with the cell cycle. The investigators hypothesize that expression of the c-fos, ODC and c-myc genes constitutes an early response to photic stimulus resulting in commitment of spermatogonia to mitosis.